Yesterday I replaced my old NIKKOR 18-55mm f/3.5 – 5.6 DX lens, that I have used for my D40 a long time ago. It broke about a year ago and I have been meaning to fix it. When at the shop they basically told me its an old shitty lens worth nothing and I should just buy a new one, cus the new ones have VR and my useless piece of crap does not. So I did. When at home though I learned a little bit more about FX and DX.
Its obvious it aint optimal to keep a DX lens on an FX camera. It just doesnt make sense to purchase a camera body with a big sensor, then putting a lens on it that is way smaller.
The fullframe huge sensor becomes completely useless that way. I understand that. But, I could help but to really like the images I got with that set up. Check these out.